Liquid chromatography (LC) is a well-known technique for separating the constituent elements in a given sample. In a conventional LC system, a liquid solvent (referred to as the "mobile phase") is introduced from a reservoir and is pumped through the LC system. The mobile phase exits the pump under pressure. The mobile phase then travels via tubing to a sample injection valve. As the name suggests, the sample injection valve allows an operator to inject a sample into the LC system, where the sample will be carried along with the mobile phase.
In a conventional LC system, the sample and mobile phase pass through one or more filters and often a guard column before coming to the column. A typical column usually consists of a piece of steel tubing which has been packed with a "packing" material. The "packing" consists of the particulate material "packed" inside the column. It usually consists of silica- or polymer-based particles, which are often chemically bonded with a chemical functionality. When the sample is carried through the column (along with the mobile phase), the various components (solutes) in the sample migrate through the packing within the column at different rates (i.e., there is differential migration of the solutes). In other words, the various components in a sample will move through the column at different rates. Because of the different rates of movement, the components gradually separate as they move through the column. Differential migration is affected by factors such as the composition of the mobile phase, the composition of the stationary phase (i.e., the material with which the column is "packed"), and the temperature at which the separation takes place. Thus, such factors will influence the separation of the sample's various components. A more detailed description of the separation process can be found, among other places, in Chapters 2 and 5 of Introduction to Modem Liquid Chromatography (2d ed. 1979) by L. R. Snyder and J. J. Kirkland, which chapters are incorporated by reference herein.
Once the sample (with its components now separated) leaves the column, it flows with the mobile phase past a detector. The detector detects the presence of specific molecules or compounds. As discussed in Chapter 4 of Introduction to Modem Liquid Chromatography, which chapter is incorporated by reference herein, two general types of detectors are used in LC applications. One type measures a change in some overall physical property of the mobile phase and the sample (such as their refractive index). The other type measures only some property of the sample (such as the absorption of ultraviolet radiation). In essence, a typical detector in a LC system can measure and provide an output in terms of mass per unit of volume (such as grams per milliliter) or mass per unit of time (such as grams per second) of the sample's components. From such an output signal, a "chromatogram" can be provided; the chromatogram can then be used by an operator to determine the chemical components present in the sample.
In addition to the above components, a LC system will often include filters, check valves, a guard column, or the like in order to prevent contamination of the sample or damage to the LC system. For example, an inlet solvent filter may be used to filter out particles from the solvent (or mobile phase) before it reaches the pump. A guard column is often placed before the analytical or preparative column; i.e., the primary column. The purpose of such a guard column is to "guard" the primary column by absorbing unwanted sample components that might otherwise bind irreversibly to the analytical or preparative column.
It will be understood to those skilled in the art that, as used herein, the term "LC system" is intended in its broad sense to include all apparatus used in connection with liquid chromatography, whether made of only a few simple components or made of numerous, sophisticated components which are computer controlled or the like.
Many different types of LC systems and components for LC systems are commercially available from a number of vendors. For example, Millipore Corporation of Milford, Mass., Beckman Instruments of Fullerton, Calif., and Hewlett-Packard Co. of Palo Alto, Calif., all sell LC systems, including pumps, sample injection valves, columns, and detectors, among other things. In addition, various columns with various packings are commercially available from a variety of sources, including (among others) Upchurch Scientific, Inc., of Oak Harbor, Wash., and Baxter Healthcare Corporation of Deerfield, Ill.
Today, most LC systems include pumps which can generate relatively high pressures of up to around 6,000 psi. In many situations, an operator can obtain successful results by operating a LC system at "low" pressures of anywhere from just a few psi or so up to 1,000 psi or so. More often than not, however, an operator will find it desirable to operate a LC system at relatively "higher" pressures of over 1,000 psi. The operation and use of LC systems at such "higher" pressure levels is often referred to as "high pressure liquid chromatography" or "high performance liquid chromatography" (HPLC).
In practice, various components may be connected by an operator to perform a given task. For example, an operator will select an appropriate mobile phase and column, then connect a supply of the selected mobile phase and a selected column to the LC system before operation. In order to be suitable for HPLC applications, each connection must be able to withstand the typical operating pressures of the HPLC system. If the connection is too weak, it may leak. Because the types of solvents that are sometimes used as the mobile phase are often toxic and because it is often expensive to obtain and/or prepare many samples for use, any such connection failure is a serious concern.
It is fairly common for an operator to disconnect a column (or other component) from a LC system and then connect a different column (or other component) in its place after one test has finished and before the next begins. Given the importance of leak-proof connections, especially in HPLC applications, the operator must take time to be sure the connection is sufficient. Replacing a column (or other component) may occur several times in a day. Moreover, the time involved in disconnecting and then connecting a column (or other component) is unproductive because the LC system is not in use and the operator is engaged in plumbing the system instead of preparing samples or other more productive activities. Hence, the replacement of a column in a conventional LC system involves a great deal of wasted time and inefficiencies.
Given concerns about the need for leak-free connections, conventional connections have been made with stainless steel tubing and stainless steel end fittings. More recently, however, it has been realized that the use of stainless steel components in a LC system have potential drawbacks in situations involving biological samples. For example, the components in a sample may attach themselves to the wall of stainless steel tubing. This presents problems because the detector's measurements (and thus the chromatogram) of a given sample may not accurately reflect the sample if some of the sample's ions remain in the tubing and do not pass the detector. Perhaps of even greater concern, however, is the fact that ions from the stainless steel tubing may detach from the tubing and flow past the detector, thus leading to potentially erroneous results. Hence, there is a need for "biocompatible" connections through the use of a material which is chemically inert with respect to such "biological" samples and the mobile phase used with such samples so that ions will not be released by the tubing and thus contaminate the sample.
Therefore, it is an object of the present invention to provide a mechanism allowing an operator to quickly disconnect or connect a column to a LC system.
It is another object of the present invention to provide a mechanism to reduce inefficiency and wasted time in connecting or disconnecting a column in a LC system.
It is yet another object of the present invention to provide a mechanism to allow an operator to quickly replace a column in a LC system.
It is yet another object of the present invention to provide a mechanism to allow an operator to quickly and easily achieve a leak-free connection of a column to a LC system.
It is still another object of the present invention to provide a biocompatible assembly to allow an operator to quickly and easily achieve a biocompatible connection of a column in a LC system.
The above and other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description of the present invention, and from the attached drawings, which are briefly described below.